The method and the associated device are intended to be used in an installation for manufacturing containers made of thermoplastic material and in particular polyethylene terephthalate (PET) by forming, in particular by blow molding or stretch blow molding, preforms. Such an installation makes it possible to produce containers on a very large scale at very high rates, for example greater than 85,000 bottles per hour.
According to a well-known technique, such containers are produced in two main steps. In a first step, molding is initiated by injection of a preform made of PET. This preform comprises an essentially tubular body that is closed at one of its axial ends, the opposite end being open by means of a neck. The neck has, right from this injection-molding operation, the definitive shape of the neck of the container. Generally, the neck of the container comprises a threading.
The preform generally comprises an annular support face that projects radially toward the outside relative to the rest of the body and that is oriented axially toward the closed end of the body. Such a support face is carried by, for example, an annular support collar that extends radially projecting toward the outside relative to the rest of the preform and that is arranged at the base of the neck.
There are installations in which the preforms, once injected, are directly passed on to the forming station, with each preform being transported individually.
However, in numerous cases, the preforms are manufactured by injection at a first location and are molded by blow molding to the definitive shape of the container at a second location in a specific manufacturing installation. Such a technology makes it possible to initiate the molding operation by blow molding as close as possible to the bottling site, with the injection operation able to be carried out at any location. Actually, it is relatively easy and inexpensive to transport preforms of reduced size, while transporting containers after blow molding has the drawback of being economically inefficient because of their very significant volume.
In the case where the injection station and the installation for manufacturing by forming are two totally independent machines, the preforms are generally delivered in bulk. The blow-molding station therefore uses a device for feeding preforms that is equipped with a device for aligning in a row and righting preforms. This invention relates to such a device.
According to a first device for aligning and righting preforms that is known from the state of the art, the preforms are discharged in bulk into a container. They are removed from this container by a lifting belt that in turn discharges the preforms at a preset pace at the upper end of the orienting rollers, also called aligning rollers. These two aligning rollers are inclined relative to the horizontal, and they are essentially parallel to one another. The two rollers are driven in rotation in opposite directions and are separated from one another in such a way as to allow an interval to exist that is of a slightly larger size than the size of the bodies of the preforms. The separation of the two aligning rollers is such that the transverse space between the two rollers is smaller than the size of the support collar located at the base of the neck.
The orienting rollers are configured in such a way that under the effect of gravity, the preforms are placed between the two rollers. Thus, by simple gravity, each preform tends to be placed between the two rollers, in such a way as to be supported by its collar on the rollers with its body hanging downward between the two rollers. The opposite rotating movement of the two rollers and their incline ensures, on the one hand, the alignment in a row of the righted reforms and, on the other hand, the sliding of the preforms toward the bottom of the orienting rollers where they are then recovered in a feed slide, itself connected to the blow-molding installation.
The thus aligned and righted preforms are accumulated in the feed slide that generally feeds a heating furnace to put the preforms at a suitable temperature for being formed.
Such a feed device offers the advantage of being able to align and right the preforms at a pace that is compatible with the pace of the manufacturing installation.
However, this known device is very bulky both horizontally and vertically. Actually, to ensure the effective righting of performs, the rollers generally have a great length. Furthermore, such devices can measure more than 5 m in height.
A less bulky aligning and righting device comprising a centrifuge bowl was already proposed. The preforms are thrown in bulk onto a rotating platen that forms the bottom of the bowl. The preforms are then thrown off by the centrifugal force against a peripheral railing. A vertical space reserved between the railing and the rotating platen makes possible the passage of the bodies of the preforms while holding them by their collars. Under the effect of the centrifugal force, the preforms are thus aligned on the periphery of the bowl, with their main axis placed in an orientation that is essentially radial relative to the center of the bowl. The preforms thus have an axis that extends essentially orthogonally both in the direction of the gravity and the direction of movement of the preforms.
The thus aligned and oriented preforms are then guided toward a tangential outlet of the bowl under the effect of the movement of rotation of the rotating platen.
Before they exit or after they exit, the preforms are righted in such a way that their main axis is oriented vertically so that they can be picked up by a travel slide, generally horizontal, along which they are no longer subjected to the centrifugal force.
The preforms are supported by their collars that rest on two diametrically opposite support points. These two support points are aligned orthogonally in the direction of movement of the preforms.
As result, the tilting of the preforms causes them to oscillate by rolling between the two rails of the slide. However, with the main axis of each preform tilting in the same plane as the support points, preforms run the risk of no longer being guided by only one support point, and even of jumping out of contact with the rails. Such a movement, if it is not controlled, runs the risk of causing a sliding of these preforms that, at best, will fall from the slide, or, at worst, will be blocked by stopping the travel of the subsequent preforms. Such a blocking is likely to cause the temporary shutdown of the entire manufacturing installation.
The righting of preforms requires the presence of guides for bodies of complex shape and adapted to the morphology of each preform model to make possible a permanent and stable guiding of each preform during the righting. Such guide parts are complex and cumbersome to produce.
In addition, when the manufacturing installation is intended to be used with various preform models based on the containers to be obtained, it is necessary to use guide parts that are adapted for each of the models that can be used. The cost of the device is increased.
Moreover, the guide-part change operations that take place during each change in preform model are long and tedious. The extended down time of the device due to this change is expensive for the manufacturer.